In 2005, Northeast states from Delaware to Maine worked on creating a regional system to limit global warming pollution from power plants, known as the Regional Greenhouse Gas Initiative (RGGI). At the outset, the states agreed to focus on reducing global warming pollution from in-state electric power generators. However, negotiators began to consider five categories of offset measures--pollution cuts outside the regional electricity sector that would offset excess power plant pollution. Cracks in the Cap explores how these offset measures would erode the integrity of the program and undermine its benefits.